The present invention relates to apparatus for preventing vortexing in molten metal as it is drained from a vessel, and particularly to a refractory element having at least one rib extending radially outwardly from a nozzle opening in the vessel, the rib protruding upwardly so as to prevent rotating boundary flow in the metal as it drains from the vessel.
In the continuous casting of steel, molten steel is drained from a ladle into a tundish and from the tundish into a continuous caster mold for solidification into a shaped product. Typically, the ladle will have a single nozzle with an opening for drainage of the steel into the tundish. The tundish also has at least one nozzle for passing the molten steel into the continuous caster mold. Regulation of flow rates through the ladle and tundish nozzles is generally accomplished by refractory slide gate mechanisms. As the level of molten steel in the ladle or tundish drops and the final remaining portion is passed through the nozzle a vortex usually forms in the steel in the region adjacent to the nozzle opening. The swirling motion of the vortex tends to cause mixture of non-metallic slag and scum with the steel passing through the nozzle. Entrapment of fine particles of slag and scum with the solidified steel adversely affects the resultant steel cleanliness. Such entrapment also causes breakouts through weak spots in the skin of the partially solidified casting resulting in interruptions of caster operation and loss of production. The entrained slag products also tend to reoxidize and deposit on the surfaces of tundish nozzles and submerged pouring tubes choking off the flow of molten steel through these critical passages to the caster mold.
Entrainment of slag and scum with molten steel also occurs during the draining of metallurgical refining vessels and furnaces. Attempts to prevent the mixing of slag and steel have included the use of stoppers which float at the interface between the slag and steel so as to partially or completely plug the nozzle or taphole opening before a significant amount of mixing occurs. Examples of such devices are shown in U.S. Pat. No. 4,462,574 and Japanese Patent Application J54042305. Attempts have also been made to specifically prevent vortexing without stopping flow of the steel through the nozzle. An example of the latter is shown at U.S. Pat. No. 4,524,958. This reference discloses injection of gas bubbles into the steel in the immediate vicinity of the taphole.
A tundish nozzle designed to prevent swirling of molten steel in the nozzle opening is shown in U.S. Pat. No. 4,079,868. The nozzle has four grooves in the wall forming the nozzle opening. The grooves extend longitudinally along the nozzle opening and are spaced approximately 90.degree. apart. The reference nozzle is designed to prevent swirling within the nozzle. However, the reference nozzle does not appear to be directed to the prevention of vortexing in the molten steel before it reaches the nozzle opening. Moreover, the reference nozzle does not have protruding portions extending upwardly into the steel as does Applicant's invention.